This application incorporates by reference the following PCT Patent Applications: Ser. No. PCT/US98/23095, filed Oct. 30, 1998; Ser. No. PCT/US99/01656, filed Jan. 25, 1999; and Ser. No. PCT/US99/03678, filed Feb. 19, 1999.
This application incorporates by reference the following publication: JOSEPH R. LAKOWICZ, PRINCIPLES OF FLUORESCENCE SPECTROSCOPY (1983).
The invention relates to sample-holding devices and systems, and more particularly to sample-holding devices and systems for efficiently utilizing relatively small-volume fluid samples.
Certain techniques in biology, chemistry, and medicine require processing large numbers of samples; such techniques include the high-throughput luminescence screening of candidate drug compounds, which may involve analyzing hundreds of thousands of samples. Processing large numbers of samples can be facilitated by packaging samples together into high-density holders, such as xe2x80x9cmicroplates,xe2x80x9d so that the samples may be analyzed together in an automated device.
Microplates are substantially rectangular holders that include a plurality of sample wells for holding a plurality of samples. These sample wells typically are cylindrical in shape, although some are rectangular. These sample wells typically are disposed in rectangular arrays. The xe2x80x9cstandardxe2x80x9d microplate includes 96 cylindrical sample wells disposed in an 8xc3x9712 rectangular array on 9 millimeter (mm) centers.
Microplates may be used in a variety of assays, including various luminescence assays. In luminescence assays, a sample is positioned in a sample well and emission light from the sample is monitored. In photoluminescence assays, emission light is stimulated by illuminating the sample with excitation light. In chemiluminescence assays, emission light is stimulated by a chemical reaction made to take place within the sample.
Although microplates are of demonstrated utility in automated screening, they suffer from a number of shortcomings. For example, sample wells in microplates and other sample holders for luminescence assays may have regions that are optically inaccessible, from which luminescence neither can be excited nor detected. Sample in such regions effectively is wasted because it does not contribute to the analysis. Wasted sample can translate into significant extra cost, particularly for assays that are performed in large numbers and that use expensive reagents. Sample wells also may have walls or other regions that are themselves detectable optically, increasing background if such regions luminesce.
The present invention provides sample holders configured to support a sample so that the shape of the sample conforms to the shape of at least a portion of a sensed volume.
The invention provides a number of new microplate designs that are useful for high-efficiency sample analysis. In one embodiment a microplate includes a frame portion, and a top portion. An array of wells are formed in the top portion. The wells are organized in a density of at least about 4 wells per 81 mm2. Each well has a bottom wall that is elevated at least about 7 millimeters above a plane defined by a bottom edge of the frame.
Another microplate design has an array of conical wells organized in a density of at least about 4 wells per 81 mm2.
Another embodiment has an array of conically-shaped wells, each well having a maximum volume capacity of less than about 55 microliters. A preferred small-volume well design has a volume capacity of 1-20 microliters.
Another microplate design has an array of wells in the top portion, wherein each well has a maximum volume capacity of less than about 55 microliters, and a well bottom that is elevated at least about 7 millimeters above a plane defined by a bottom edge of the frame.
A further microplate embodiment has an array of wells in the top portion, organized in a density of at least about 4 wells per 81 m2. Each well has a conical portion characterized by a cone angle of at least about 8xc2x0.
Another microplate configuration has an array of wells that are conically-shaped and characterized by a cone angle xcex8 wherein xcex8=2arcsin (NA/n), NA being equal to or greater than about 0.07.
Another microplate design has an array of wells organized in a density of at least about 16 wells per 81 mm2. Each well has a frusto-conical bottom portion and a substantially cylindrical upper portion.
The invention provides a system for detecting light transmitted from a sensed volume. The system comprises (1) an optical device capable of detecting light substantially exclusively from a sensed volume, and (2) a sample holder configured to support a sample so that the shape of the sample conforms to the shape of at least a portion of the sensed volume. The sample holder may be a sample well in a microplate and may have a conical or frusto-conical shape, so that the sample conforms to a portion of an hourglass-shaped sensed volume.
The invention also provides a microplate comprising (1) a frame, and (2) a plurality of frusto-conical sample wells disposed in the frame. The sample wells may be characterized by a cone angle of at least about 8xc2x0. The microplate further may include a reference fiducial that provides information to facilitate sample analysis.
The invention also provides methods for improving signal detection in luminescence assays. One such method comprises (1) selecting an optical device capable of detecting light from a sensed volume, (2) selecting a sample holder having a shape configured to conform to the shape of the sensed volume, and (3) performing a luminescence assay using the optical device and the sample holder.
The invention will be understood more readily after consideration of the drawings and the detailed description of the invention that follow.